Question

I declared a template for a class and I am trying to use that class as a vector in the subsequent class.
Here is my code:

#include <iostream>
#include <vector>
#include <utility>

using namespace std;

template <typename L>

class AdjacencyListVertex {

public:
    L data;

    vector<int> edges;

    AdjacencyListVertex() {
        data = -1;  
    }

    AdjacencyListVertex(L _data) {
        data = _data;
    }

    void add_edge(int other) {
        edges.push_back(other) ;
    }

    void print(int i) {
        cout << "  vertex[" << i << "] '" << data << "' connected to:";
        for (int j = 0; j < edges.size(); j++) {
            cout << " " << edges.at(j);
        }
        cout << endl;
    }
};

template <typename L>
class AdjacencyListGraph {
  public:
      vector<typedef AdjacencyListVertex*> vertices;

    AdjacencyListGraph(int size) {
        vertices = vector<typedef AdjacencyListVertex*> (size, AdjacencyListVertex<L>());
    }

    void add_vertex(int position, L data) {
        vertices.at(position) = AdjacencyListVertex<L>(data);
    }


    void add_edge(int vertex1, int vertex2) {
        vertices.at(vertex1).add_edge(vertex2);
    }

    void print() {
        cout << "AdjacencyListGraph:" << endl;
        for (int i = 0; i < vertices.size(); i++) {
            if (vertices.at(i).data != -1) vertices.at(i).print(i);
        }
    }
};



int main(int argc, char** argv) {


    AdjacencyListGraph<string> alg_str = AdjacencyListGraph<string>(5);

    alg_str.add_vertex(0, "alg_str vertex 0");
    alg_str.add_vertex(1, "alg_str vertex 1");
    alg_str.add_vertex(2, "alg_str vertex 2");
    alg_str.add_vertex(3, "alg_str vertex 3");
    alg_str.add_vertex(4, "alg_str vertex 4");

    alg_str.add_edge(0, 1);
    alg_str.add_edge(1, 0);
    alg_str.add_edge(1, 3);
    alg_str.add_edge(3, 4);


}

I keep getting the errors:

graphs.cpp:38: error: template argument 1 is invalid
graphs.cpp:38: error: template argument 2 is invalid
graphs.cpp: In constructor ‘AdjacencyListGraph<L>::AdjacencyListGraph(int)’:
graphs.cpp:41: error: template argument 1 is invalid
graphs.cpp:41: error: template argument 2 is invalid
graphs.cpp: In member function ‘void AdjacencyListGraph<L>::add_vertex(int, L)’:
graphs.cpp:48: error: request for member ‘at’ in ‘((AdjacencyListGraph<L>*)this)-    >AdjacencyListGraph<L>::vertices’, which is of non-class type ‘int’
graphs.cpp: In member function ‘void AdjacencyListGraph<L>::add_edge(int, int)’:
graphs.cpp:55: error: request for member ‘at’ in ‘((AdjacencyListGraph<L>*)this)->AdjacencyListGraph<L>::vertices’, which is of non-class type ‘int’
graphs.cpp: In member function ‘void AdjacencyListGraph<L>::print()’:

Its an error in the line:
vector vertices;

What mistake am I doing in the definition of the vector?

Answer 1

You got the syntax wrong. Were you just guessing some keywords?

You need something like this:

std::vector<AdjacencyListVertex<L>*> vertices;

Maybe what you meant was to typedef the list type:

typedef AdjacencyListVertex<L> ListType;

std::vector<ListType*> vertices;